Signaling system



July 18, 1933. E. H. SMYTHE I SIGNALING SYSTEM 3 Sheets-Sheet 1 Filed Jan. '22, 1929 July 18, 1933.

v1:. H. SMYTHE 1,918,433

SIGNALING SYSTEM Filed Jan. 22, 1929 3 Sheets-Sheet 2 "3 SheetsSheet s E. H. SMYTHE S IGNALING SYSTEM Fil ed Jain. 22, 1929 July 18, 1933.

' My invention relates to signaling systems employing high frequency waves as 'the'" me-; dium of commun cattonfand mere partlcu i'arlyto the 'selectlve 'receptlon and amphfi-- It is Well nown that signal earner ay'es;

under favorable conditions, l ney he' received with a high degree of-selectlvlty when" subwave ofappropriiitefrequency. It ise lso Well known that tl' lere ate W efiect at tenhmtupon "this*t ype"ef'c I ceutien which 3821a to treublesemeinterfeb'a eh c-e betw en, stations'. Thel= moduleting received frequencies plfotlilces side frequem .cies each 'efwihich carrieskt signaling-feeq'uency cempon'ent' 'WhlCh sldes f reqpenclesv may cause iii'tel'fflellcqbQtWGQIlfStfltlOQS to a ;g-reater extent than the conesjpcndmg '0 1'1g1,

- I 'tinctsetti'ngs of the "selecting inechamsmd of and means for receiving-carrier Waves with highdegree of selectivity'and freedom from ihterfercnce threnghout a w1de freon of the ee fri'er wzwesfrom aplul elit y 1'1 er"( ch statiohfto zt sjngle s et m the when selecting devqce t meduvyaves in such a Way; its] to,

iiivc fl in modulation, to effect amplificadtienj efthe Tl ecelly gcnefated Wave of fiXGd frequency yzplue; 'llu SQ rotate the frequency of the 10- why generatedmedulatmg QwcVe tethe fre- 6. m? Y M qljlepcies ceni p 'i sedf injthe plurality of heterodyne meduhitieh's'f td effect imlti stat'ge heteredjhe' "implific ation by means of the, same locally generated 7 i-way'eg: tc fefiec't; amplificatie'n gwithf accefn" ected t0 modulation withja ldcally generated effect nmltiestage emplific zttionfl cf pertieu ere tuned to diffel ei' t frequehcie s; tegrel a'te action between thelocally; geilerzited'-andith' orj subst ant-tally p f eventithe mdiatieh-ef'the 51ml leilelvdWavefIBqUQHCISr In many re; ceiverr; empleyin they-so-cailled superheterpereinthis statiniis I I r 111g Waves and the locally gene'ratd'mqduhi ,lng {wave ,al'e, so v chosen] 1h "relation to jeach fre 'uenc "relaltionvwith'res ectwt e whlle at the same tn ne hmltlng p th suppliedywaye; is, minimized? Or eliminated t. cf th modulatorarepieferably n'oneover :z-cnce by undesiredproducts of l Ppi fig a betw een stations, and'inthenei'gh;

I borhocd of the received, fre'q'uency r ange'zso rcceivefi \"va'ves by mcduletingthesame with mezthsef elementellaving constants WhiQhjaIe" I similapto these of the elements me :for selecting the incoming waves; The methods) :Ser aLmdQ234,281,

panyingiehalige of ipequehcyih Serdei tep'ei' ihit selectiife tuning: jwhile caveidi l lfg the v tendency to fe'ed back. and: oscillations t 1&1 car ier Wave 7 whic'lt siiccessive stages 10 eallyfgenemted.WEWQ; and g nerally tbqima pre-ve antl; prepe ly coordinate th relation 6f :theflocal and received {wave "frequencies and, the apparatus futilized in different; part8 of a heterodyne Waver'ecmwhg systemi t In accordance with one aspectef thejpl st i othe that no interference cap takepplace b tween the selected sidefrequency}tefgflieidee J siredetation the side fi'equehciee ,of the I I other stations, er between groups" offside ban ds; which it i's desire keep separated. Only Zone setting. of the selecting mechanism 'can'selects,staticn efgiven frequency; and no other statien cz tn be selectedbynthiese The s icle. frequencies utilized from -the. 0u tpi1t astohe susceptible e'f cenvenient-contrdl by v and means of my invent-ion are adapted for selecting waves from any desired. frequency posltlon withinawideband'of incoming Wave frequencies. Vlhen the receiving circuit is OI'ga-IIIZQdJH accordance With certain features of my invention, this band may haveawidth as large as one ofthe Wave frequencies With in'the' band.

The 'localosci'llator'frequency shouldp'ref I range, but may be either-above'orbelowrsaid erablybe outside of the received frequency range, and may also lie Within said range providedcertain other requirementsare com-" plied 'w1th, as' Will hereinafter be pointedout. quency is below the received frequency range and the difference frequencies of modulation areto beutilized, the received-range in'cer tainmodifications of the application of my invention; should be limited in Width to a value not greater than twice the minimumfrequency in said range. The oscillatorfrequency in this case should be not jgreater than Qthe minimum frequency in thereceived frequency range, and should be not less'in value than one-,half'the frequency vvidth of the receivedv range.

=By subjecting theincoming carrier Wave eneigy 'to one or more heterodyne modul'a sired selectivity characteristics, the desired: slg-nalbearing-earner Wave energy maybe tions, at least-one bfwhich provides the deefficiently translated into Waves. of convenient frequency freefrom feed-back and'selfoscillationtendencies. The-heterodyne modulationor modulati-onsat the same time may beemployed to increase the energy of the a Wave s{tl1at it is desired to utilize without depending therefor upon cascadeamplification 2 With itsinherent tendency vto cause "energy a-i' variable selective output adapted to have maintained between them a tuning frequency difference equal'to, the frequency of, the '10- cally supp'hed modulating Wa ve. In the WellknoWn superheterodyne system, for instance,

the selective input to the 'jmodulator is vari- Cable with respect to frequency, the selective [output is-fixed, and the local modulatlng frequency is'variable. In the present invention the selective input and the selective output oiarebothvariable and-the local modulating fixedf frequency outside the i received frefre uenc is fir; d. A ain in thesuJerheterodyne system the. locally generated frequency a frequency tuning range In the present-hr" is a variable frequencywithin the received vention the locally generated frequency is a 'quency tuning range. a I

-' l\lor-e'broadly,thcapplicationof the prim In case the fiXe'df local" oscillator-freciple of the fixed heterodyne modulation and amplification, as hereinafter more particularly described, may involve merely the impressing with or Without preliminary individual selection of all ofthe received carrier Wave or. station frequencies upon theinput circuit of the modulator tov which the local fixed frequency isapplied, and the selection of any or all of the upper side band frequencies of the received aves or the selection of any or all.

of the *lowerside band frequencies of the aves in the output circuit of'the modulatoror in a' circuit operatively associated there- ,Wlth; The sel'ectedrange of upperor lower 1 v v side band frequencies includes an amplmed carrier Wave corresponding to each' carrier 'or therange of modulated aves or aselected individual Wave may again be actedupon by the loca A'ed frequency in asecond stage of modulation and the resultant side band fre-. quency or frequencies, thus further amplified Wave lying Within the received range',.and-the corresponding station frequency may either 3 be individually selected and further amplified.

and'detected' atits changed frequency level, 1"

in "energy: vand restored to the origlnal frequencyvalue of'othe originally received Wave or waves, maybe-subjected to further amplilication and detection in the ordinary Way.

; There are many advantagesresultingfrom the lixed heterodyne(amplification of the re 5,ceivcdicarrier aves vvith attendant change in, frequency level Which may be secured in accordanceith the principles of my invention-"and the employment ofthe methods 1 and organizations hereinafter to be setforth.

Amplification being accompanied by change of frequency level, the tendency to objection,-

having an invariablevalue dependent upon the fixed frequency ofthe local osc llator, the

mechanically coupled and coordinated. "The signal bearing. frequency values operating ithin'the receiving circuit maybe setland prcdetermlned by the frequency value assigned the local-oscillator to such values as .Will minimize 01- prevent interference be tween stat1ons; and may also be adjusted to sucha level as to take advantage ofthe most favorable amplification factor in the amplifying stages Whichmay succeed thestage or stages in which the heterodyne amplification These and othenadvantages which arise whichz v F 1 are, inclusive, are vcircuit diagrams of Wave receiving and'utilizing organizations embodying the various features of*7.ll

, able feed-backof'energy is avoided. The Y frequency level difference between stages tuning elements successive stages may be.

llf)

from the employment ofthe variousfeatures of my invention-[Will be: understood more clearly in .vieW of the following detailed. de-. scription and the accompanying drawings, in r ference'side frequencies lying very close to the frequencies of the received Waves R c which give rise to these side frequencies, the

station 3 frequency of 1,000,000 cycles being 5 identical with the side'frequency 1,000,000;

Under these conditions, unless nieansare provided for preventing-it, there will be a ing conductor as in the case of Table B.

wl ablol) shows the relationship of th'e' wave I frequencies in the ordinary superheterodyne.

type of re lver "wherein the oscillator frequency'li' is varied in order to produce the same difference .sidefrequencies for each station frequency, R, these sidefrequencies havmixed valueof 50,000 cycles. It will be A v a that'station 1 may be selected by adjustingfrequcncy K, to either 1,550,000 cycles or 1,450,000 cycles, the fixed difference frequency 50,000 cycles bein produced in each i Q fllnrthermore, Whenthe oscillator frequency K,-is adjusted to 1,450,000. cycles,'staliens 1 and 2 both appear in the output of ie modulator on the 50,000 cycle difference frequency-Waves, and thus interfere. Simiinterference and .multiplici ty of settings of the selecti mechanism arise in connection with each setting of the oscillator frequency K. circuit of the modulator can preventinterferi-n'ice betvv'een ti'o stationson any given setting of the oscillatorfrequency'K, but such tuning ofthe modulator input, of no value for reducing the multiplicity of settings of the station selecting mechanism.

Table E shows a relation of Wave frequen cic; which may be employed to avoid the interlerence and lack of selectivity of the lrin ds referred to above. The received frequency range has a Width equal to one of the frequencies Withinthisrange; that is, 050,000

cycles, this range being limited-in Width to i a value not greater than twice the'lowest frequency Within saidrange. It Willbe observed that the oscillator frequency K of 500,000 cycles close to the received frequency range but spaced sufficiently below the received range to make it feasible to de tune the recei ingcircuit to prevent any tendency of the Waves K to escape. It will also seen that the oscillator frequency K, in

I this: case isgrea'ter than one-half the firequency Width of the received range.

, l l avesof frequency K, voff500,000 cycles, in Table E, modulate With the incr uning Wave frequencies R, thereby: producing side fre quencies of one sign which do .i'iot'interfere with ea'clijotherby coincidence of their free- C11l611ClQS, l1lfl.(-i() not interfere by coinciding in frequency Withside frequencies of oppo-c site-sign.

7 i-ne band of difference side frequencies RK, extends from 50,000 to 1,000,-

000 cycles and is spaced 50,000 cycles, a conrrc'qucncy scale to the range of received fre- Unly sharp tuning of the input receiving venient amount to permit ofdiscrimination,

from the band of sum side frequencies R -l- K, extending from 1,050,000 to 2,000,000icycles. It will be noted that bothba-nds' of side f equencies are as close as practicable mum qucncies' R, of 550,000 to 1,500,000 cycles, thereby avoiding the use of extremely high or extremely low. Wave frequencies, and thus being susceptible to convenient control. The

separation of 50,000 cycles between the frequency of the locally supplied Waves K and. v

the lowest received frequency B, provides a suitable margin tofprevent the Waves K, from reaching the antenna or-vinput circuit of the modulator and causingobjectionable escape of the Waves K, to disturbneighboring stations.- The value of the locally supplied wave frequency K, in relation to the received frequency 'range'is-such that no side. frequency coincides-in the frequency scale With the corresponding station frequency from which it is derived. Either the sum or thedili'crence side frequencies may be selected from, the output of the modulator for further utilization, Without incurring interference between s 'm s and Without resorting to special timing of themcdul'atorinput to :sep- .arute Wave frequenc es,

Within the limits of the received rangefl it will notedthat both the sum and dh'l erence side frequencies overlap over part of their. range Wltltt part of the received frequency range. 0 Possible effects due to such overlapping are prevented in certain embodiments of my invention, hereinafter to be described, by employing a modulator of the carrier suppression type. In other forms ofmyinvention, as Will here'- inafterappear, overlapping is permitted but interference effects are prevented by coordinated tuning of different stages of the circuit at dilferent frequency' levels.

Referring now to the Wavereceiving -cir-- cuit shown in Fig.1, the radio 'loop' antenna 10 is tuned by a variable condenser llto interference selectively receive signal carrier Waves R of the desiredst'ation frequency. The selected Waves are transmitted to thecommon or parallel input path 12 of balancedmodulator 14 of the kind described in the Carson Patent No. 1,343,300; Oscillator-16, which is shown as being'of the W'Gll-kHOWHIIQLItlQY type, but

sary to keep the oscillator adjusted to-the desiredfixed frequency after it isonce set for that frequency. l Vaves from oscillator 16 are piclredupby the coupling coil Which Lmay have only such capacity as may be neces-v forms a part OflJIElDSfOZIHG/P'lS and are ap- I plied throughthe medium of transformer 21 i to the seriesinput paith13 of modulator 14.1"

The characteristic relationships I whichexist in the balancedmodulator 14 are such of transformer 27 to the as to produce in the'secondary windingof the output transformer signal carrier waves of frequencies lt-K and R-F'K produced'by frequencies of only one sign andsubs'tantially" to suppress waves of other frequencies. Net

work F may be a high pass or a low pass.

filter. The selected waves R-IC orIH-K are transmitted through transformer 23 to;

the series input paths 2 1 of the balanced modulator whicli'is similar to modulator 1 1. Locally generated waves'froin theoscillator 16 are carried from a pick-up coilloii oscillator transformer 18 and applied by way 27 of modulator 25: r i a y Resulting waves, produced by modulation in modulator 25, are-transmitted through transformer 28 to network F which is preferably aii'electrical filter of similarjtype to thato'f network F Network F may, in

an assumed. case, be designed to pass signal bearing side frequency waves of only one sign, and of the same frequency as thewaives' selectively received on antenna 1O, it being noted that-modulator 25 combines the locally generated waves Kwitl tho side frequencies l t- K or R+K selected by network 22, i The l side bands of the received carrier waves the. sum products of the second 1110(ll1l2tl310l1211'6 v of a frequency corresponding to the original result of: this second modulation is to produce other s debands of which eyer signal bearin side bands have been passedthrough the precediiiu electrical network F If the v w 7 1 1 1? i v network I nas been. chosen to pass the lower received frequency; and if the-selective net work F has been chosen to pass the upper side bands or sum products of modulation,

the lowenside bands'or difierence products of the second stage of modulation ai e'of the original received. carrier ii'equency. Thereare other frequency ;oroducts tot the second stage of modulatio in modulator 25 but these are either neutralized or suppressed in the output circuit of the balanced modulator itself or are suppressed in the selective net work orelecti'icalfilter F 1 The signalbearingcari'ier waves of frequency Rare selectedby the network F and ai'e'transinitted byway of transformer 30 to the input circuit 31 ot detector 32, which may be of any well known construction. The detected waves of signalfrequency, 'which are of the ordinary audible frequencies,'maybe parallel input path transmitted-to a loudspeaker 33 to produce an "audible signal or may be. utilized in any i other desired manner. "Anamplifier 34 may I be inserted, if.desired, between detector 32 and loudspeaker 3jto amplify the signal waves 9 l -The circuitof Figil has described thus far as requiring the adjustmentof-only one. tuning element; antenna condenser .11,

inorder to select anydesired station, The

selectivity of the circuit maybe increased by connecting variable condenser35lwith in put circuit 31 of detector 32; "Circuit 31 may.

thus be sharply tuned. to'the-same frequency B as that'for which theanten'na '10 is tuned.

VVl-ien condenser' h is employed, suilicient' scl ectivity may be ohtainedwithout" employing network F For 'conveniencein adjustment the mechanical coupling 37 may be provided :8

to connect the movable elements of'the two condensersl land 35; sothat the movement of the coupling synchronously adj ustsboth condensers andmaintains circuits1O and 31' tuned to the same frequency. Y

AS iswell known,"modll fi Gift-tilde tl'pe described, wherein a received carrier wave is caused to interact withaalocally generated oscillation, has the efi'ect not onlygof"changing the frequency level of themodulation,

edwaves, but also of greatly increasing the] voltage ofthefpro'd'ucts ofmodulation. The

result therefore in the circuit that has been described. is not only to in crease. selectivity as between" simultaneously a received waves of different stations, but also to .efi'ectgin the two 1 stages. of modulationda largev voltage amplification'of t'he received s'ignal 'bearing carrier wavefan l y 0 tages of modulation wit v the "same locally generated frequency the se lectedand amplified signal bearing carrier wave reaches the-detector at itsoriginal ;re- Y ceived frequency value. "The. coupling circuits by means ofwhichthelocally generated" "n 7 oscillations i are applied to] the moi'lulators are shown variable with respect to thedegree of coupling employed in order that thelo'cal l ly generatedjoscillation may-be applied to themodulators at the correct voltage to secure products of modulation.

' When the receiver shown 1 ment so that circuit 10 may beltuned ohlybe! n Fig.1.is adjusted in accordance with Table E condenser .11 is'preferablygiven fixed limits of adjust- 12o a tween thebroadcast frequency limits of 1,500 and550 kilocy'cles, the oscillator .16 being ad justed tosupply waves K of .500 kilocycles; The trimmer condenserf17 in this case may be only such adjustment as" would keep the fre quencyof the oscillator at approximately'500 kilocycles Anygradual change likely to ocour in the frequency of; the oscillator doesnot aifecttheoperation of the receiver'as the cf? 3 roducts of the received and locally g ra; 95 v maxim-um amplification of the resulting 1 p merely averiiier c ndenser, which may have column R+K.- "Vaves selected by networr: 10

. fect' ofany such change is automatically compensatedin 1nodulator25 when the carrier wave energylsj restored to its original frequency R. Network F may be. designed to i'tran'smit difference side frequency waves shown in column R-K, and suppress all other frequencies, or it may be designed to transmit only sum side frequencies shown in F are combined in modulator with waves of frequency .K, thereby restoring the signal carrierfwave energy to its original frequency' R.

In the "modification illustrated in Fig. .2

"it may be assu'medzthat the si nal bearing carrier waves R received upon the antenna 36 are withm. the-usual broadcast range'of 550 to 1,500 kilocycles. The antenna is-connected directly with the common portion of the input circuit of a balanced modulator M of the type hereinbefore referred to,-a radio frequency choke 42 being .included'in the common circuit between the antenna terminals. A'locally generatedwave K,.-which' may in the present instance be assumed to have a frequency of. 500 kilocycles, is applied from oscillator O to the series input circuit of the balanced modulator by way of an inductive linkcircuit, the coupling of which is'made adjustable. As a result of 7 the intermodulation of the received waves R and the locally generated wave K, there appears in'theoutput circuit of the modulator the amplified sum and difference products of modulationand the amplified locally generated wave. I

- In the present instance the electrical filter F connected with the output circuit of'the modulator has its elements so proportioned as to act as a low pass filter adjusted to transmit frequencies up to and including 1,000 kilocycles and substantially to suppress the products of'modulation lying higher in the frequency range.

Consequently the lower side bands or difference frequency prod ucts of modulation of the locally generated wave with all of'the carrier waves received upon the antenna are transmitted through the filter F and as the locally generated frequency lies within the transmission band of the filter, that also is amplified and transmitt-ed, for use in the second stage of modulation.

with their intensities increased by two stages to the loud speaker.

of heterodyne amplification under circum stances, as explained, which prevent the transmission to the radio frequency amplifier A of more thana single signal bearing car rier wave for each station.

The input circuit of amplifier. A is providquency components of this wave are detected 6 in detector D and hence may pass through the usual audio frequency amplifying stages The detector D is also, provided with a tuningcondenser 45 which,

. if desired, may be mechanically coupled to and coordinated with the tuning condenser 43 associated with the amplifier A.

As will appear from the foregoing, in the circuit of Fig.2the broad station, selection is effected in the electricalfilter F which is adapted to pass only one of the sets of side means of the tuning circuits controlled byv the condensers 43 and 45.

In the form of the invention llustrated in Fig. 3 the carrier waves received by antenna 10 are limited in selection by condenser llt-O the desired range of frequencies R, which maybe the broadcasting range of from 550to 1,500 fkilocycles. oscillator 16 is set to generate-a 500 kilocycle wave K, below and just outside of the range of received frequencies, the selected carrier frequency and the local frequency of 500 cycles are transmitted. to the input of modu lator 38, the output circuit of which modulator contains the primary winding of transformer 39. Variable condenser 40, in. shunt with the secondary winding of transformer 39, tunes the input circuit of the modulator 41 to the frequency of the modulation product of the particularcarrier wave that has been selected by antenna tuning condenser 11. Assuming that the-selected stationcarrier is one that has a frequency of1,500kilocycles and that thetuning condenser 40 is 1 such as to give it atuning range covering the upper or sum side band frequency of the various received stations, then the condenser Assuming that the local 1 40- in the assumed case will be adjusted to This 2,000 kilos cycle wave therefore flows in theinput circuit of modulator 41 together with a 500 kilocycle wave K derived from the local oscilla-' tor 16,- The 2,000 lrilocycle wave and the locally, generated 500 kilocycle wave thereuponintermodulateto produce 511111 and (hf-.-

ference frequencies, yvliichfiowin theoutput circuit of modulator 41and are communicated through the output transformer to the input circuit of detector 32. (The input'cirw cuit of detector 32-sis providedwitli a tuning condenser 415 having a rangeadapted to-en' able the input circuit of detector 32 to be tuned for Waves of frequencies between 1,500 kilocycles and 550 kilocyclesr In the case that has been assumed, the difi'erence product of modulation of the 500 kilocycle local frequency andthe selected 2,000 kilocycle carrier side band in the second modulator 41 has a frequency of 1,500 kilocycles, which is r the original frequency of the signal bearing frequency amplifiers A uand to the jlOllClcarrier Wave for Which thelantenna 10 is as suined to betuned. After ClGlTlOdlllEttiOIllIl the detector 32 the signal or"audio frequency components are carried through the r audio speaker S.

' It Will be noted that there a fixed tuning difference between antenna'tuning condenser 11 and tuningcondenser 4O which is'equ'al to the frequency Value of thelocal oscillator '16,

and thatthis saline tuning difference exists bet-Ween condenser 40 and condenser" 45, "tl1e' tuning [range of condenser coincidi11g with that of condenser 11. These three' tu ning condensersmay therefore be mechanically coupled "together and coordinated in their tuning nioveinents,and are so indicated iiitlie drawings. The mechanical coupling of tuning condensers is well understood in the art,

and it is-thought unnecessary to'show any specific means for accomplishing this result;

It will benoted that the tuning coordination of the condensers may be accomplished by the propershaping of the plates of their moy able or fixed elements'or by establishing the proper gearing relations betweenithe inov I able elements, "or inhanyot her Wellknown Way. It is also ohvious that the coordinated variation of the tuning ofl the stages of the a circuit mayif desired-be accomplished set;,

ting up the" required relation between i11 ducltance rather than capacitytuningfi ele ments or by proper combinations of i'coordi-- nated niovablecapacity and inductance 'ejle inentsh In the particul'ar casejassunie dthe tuningrrangc ofthe:antennacondensertiis':

betWeen'550 kilocycles, and 1,500 lrilocy cl e'sf. Therefore the tuning circuitrcjontrolled s by variable condenser 45- Will have this same range, andthat controlled by tuning con?- denser {iOfiVillhave a range equal to the sum or difference between this" ,i'an ge and the fixed frequency of the oscillator 16. If the o'scilg lator' frequencyis assumed to be500-kilo c'yclesjand the sum products of modulation are to be selected' by thejt'uning circuit of i Variable, condenser 40,- then that] tuning circuit will be variable' yitliin fajrange value of the 1 11161117 of the oscillatorf". a i

In the circuitiiorganization; of Fig, 8 that hasjustlbeen described'the locally generated fwave was assuniec'l to have a frequency alue denser 40 on the other hand will ten r-re; i

spondin'gly less? Whateyer the frequency u a ocal oscillator '16, 1nay'be",-the

always be setifor identical frequencyrangesii tuning circu fof. condensers" 11 fand 45firill If there isl'any slight'changei-n'the frequency ofthe Waye generatedybyi oscillat r' 16 tend-' ing to alter thefrequency ya-lue of t the side band for which variable condenser: 40 is co- I ordinately set in the tuning operation, this- ,n aybe corrected by occasional-slight adjusttiin lliili condenser if: of :tl ef lying slightly, below. the lowest carrier free quency' of ,tlie receiyed" range, and the? sum 01: upper, side band frequencies Were assumed tobethose selectedandfutilizediin the output circuit of the first modulator. Ingmar rangement ofFig."' i, whichiwill-now be d e- 1 scribed, it is assumed that the locally {gen-i ei'ate'd Wave has a frequency value above the highest frequency of tliecarrier avefranfgep a and that the lower side band,ofjmodulation 1's selectedan'd util zed in'the output circuit of the first modulator. Inthiscircuit-thecare rier Wares are received the *antenna A4; H ;\Vl1lCl1 isselectively tuned for ajparticiil'arf station by"the-variable condenser-45. :The selected, carriei'i nque e R I is [applied to Q the. divided input circuit of balanced inodu lator hile at the sain'e time the locally 1 generatedlwave K f 'oin r oscillatorfO is. apQ-f plied to thelseries input-circuitof the mod-u r later; These two "waves inte nod ilate and theirsuin and ldiffei'ence products appear, in the :output circuit: of the modulators In the, 131838115,lllSiltlllCewlt may be assumed, for e ample;thati-thei locally generated aite has a frequency; of 2,050 ki'loc-ycles; "If the se-fl lectedlicarrier Wave hasa frequency of "550 j killocyc lje'si the difference productlof ino dulafl tion y'v ill have 'a fijequ e' icyj of 1,500 kilocycles, -Ifr'the'seleotedcarrier Wave, 1,500 kilo 'cycle way e the difference product of.'inodu-} requency/yalue of 550 'kilocycles. [The difference-productsof modu: 1

\ lationf selectedfland utilized iiijtlie output 20f 'i'n o dulator- M therefore extend oyerthe sanie v u frequencyYrange as i the original carriers: a Y

latilon willflhave a.-

themselves, Qbut in an inverted relation' to thecarrier frequencies. 'flhe;highestf'receivd 1 a carrier frequency corresponds to the lowest utilized modulation frequency n the modulator output circuit, and the'lowest received v carrier frequency corresponds with the highest. utilized nodu'lation frequency in" the out- I put circuit, and the intermediate frequencies in the range. are similarly represented by complementaryfrequencies in the output range Therefore if, as shown in Fig. 4, the station selection associated With-theinput and output circuits of modulator M is accomplished by means of tuning condensers,- the movements of themovable elementsof these Condensers are so related .that as the capacity of theiiriput condenser is increased, the capacity cfthe output condenser is correspondingly decreased. ,Hei c'e the two con densers may be, and are indicated as being,

- 3 mechanically coupled-and coordinated to operate in this Way."

The tuning condenser 46 that controls the selection of the agproprate modulation product of inodulatorltfiis connected in the input circuit of amplifier After amplilication in amplifier Aftheselected Wave is ap plied to the input circuit of detectorl) and the detectedaudio frequency components of the selected carrier Wave may then be amplijfie'dfin audio frequency amplifier A? andconv-eyed to the loud speaker S. Additional sellectivity with respect to the selected carrier Wave may be secured bythe tuning" condenser 47, associated with the'input circuit of detectorD and this variable condenser may also begmechanically coupled. and coordinated .With the tuning condensers and 416, as indiouted. 'lhe tuning effected by condenser 47 in- 'thesamescnse as that effected by condenseilfi, and both of these are inan opposite to'the tuning movement of condenser 41' V ;.lliis indicated-in" the drawing by the, direction of slant of the arrows wh ch 1ndicute Variability of the conden'sersr At some point as tuning. controlled by condenser 45 1s var eddownwardly and that controlled by, condensersfi mm? is yaried upwardly or vice versa, a pr'iint is reached Where the input and output circuits of modulator M are tuned to the; same frequency. But the tendency to osc llation which might otherwise occur when this condition is 1' reached iii-prevented by theconjugate relation existing in the balanced modulator between the parallel relation ofthe antennalin- ,'piit circuit andthe series relation of the l11 OClulator output circuit controlled by condenser 46. By'making the frequencyyalue -ofvt-he ilocall venerated Wave :of oscillator O suiii y D 1 J i products of modulation lies entirely above the 'freouenc 1 ran e'of the received oscillations which can be done by making the. frequency of the locally generated lVZI VQ slightly'over 8,000 kijlocycles,such coincidence between the resonant frequencies of the. modulator input and output'circuits may be entirely avoided;

- In such case the timing ran ge of the antenna input circuit. would remain as is, between and 1,500'kilocycles, While the resonant 1 V 550 circuits controlled by condensers-l6 and 4:7. would have a range extendlng approximately from 2,500 to.1,550 kilo'cycles.

t Will be noted thatin the clrc iitz of l there is but a single stage of heterodyne modulation and amplification, that which occurs in the modulator M. In the-arrangement of Fig. 5, which Will now be described;

there is also but a single stage of heterodyne modulationand amplificat on. The received carrier Waves in thef broadcast range are circuit of balanced modulator M aradio frequency choke e9, asin the circuit ofFig. 2, ,7

being inserted if desired. A locally generfated. :WRVQ from oscillator O isapplied to the.

'80 picked up by antenna 48 and applied, with out individual tuning, to the divided input series inputcircuitgof balanced niodulator f ids, and the resultant products of modulation are communicatedto radio frequency ampli- I i also has associated with it a tuning condenser '5). From detector-D the audio frequency components are amplifiedin audio frequency amplifier A and may then be communicated toloud speaker S.

As a result of the intermodulation of the received carriers R and the local Wave Kin modulator M there are produced in the'out put circuit of the modulatortl e sum and difference products of modulation ofthe tWo; If it is assumedthat the locally gener ated Wave is given a frequency Value, say

500 kilocycles, Which isgre'ater' than half the frequency range (950 kilocycles) of the received. frequencies, then therange of side i band frequenciesrepresentingthelsum prodquency'sidebands representing the difference products of modulation, and the aniplified carrier Waves of the original received;

I nets of modulation are entirely separated from and non-coincident withthe lower frefrequency-values are suppressedin the out-.' 1; i

put circuit-of the modulator. Assuming. 500

lrilo'cycles for the local oscillatorfrequency I an'd 5' 50 to l,500;kilocy cles for the ranges'of' received frequencies the. upper 1 side, band products of modulation appearing inthe output circuit'of modulator h 5 cover, a range extending from 2',QO0 *to 1,050 kilocycles, lnle the lower side band products of modulationcover Ia frequency range extending from 1 ,O0O kilocycles to 50. kilocycles. Air

suming inthe. presentinstance that the up} per side band frequenciesare 'to be used, the tun ng condensers 49 and 50, -Wh1ch are. 1n-;

adapted to apply a lesser partjofthe vol drop'to 't he input-circuit of modulator As the control circuit 56 of the oscillator O? is .resonantonly for the frequency whichthe oscillator is set to produce,'the circuit 56' presents a low impedancepath to 1 any frewhich maytend to'be fed back by way of the.

quencies other than I th :ios'cillator frequency tap connections from the "circuits of the two M and'M and therefore tends-to modulators operate to minimize orprevent any feed back 7 or coupling between the two modulator 'cir "cu'it's. f It be noted that in any ofthe arenas; described wherein two hete'r'odyne iino'dulators are supplied from the same local oscillator, any "possible tendency for feed back or cgupiin 'between the two mayre adily beeliminated by the inclusion of an electron a 'tube'amplifier iii-one of the local Wave supplyingbranches', prefer-ably in the branchto the second modulator where the voltages of a thecarri'r wave should preferably'be greater "thaninfthe input circuit of the first modula In the 'oircuit of Fig. 7 the "carrier waves are picked-up by the? antenna which is tuned bysinea'ns of the variable condenser 61 to comprehend the desired, frequency range.

The tuned antenna circuit "is included 'in tl e input circuit of modulator M which derives its'locally generated wave by way, of tap '60 from the oscillator O 7 The I output circuit 1 lof modulatoris connected with the'inp'ut: "circuit of modulator-M? in which there in "cluded the variable tuning condenser 62" that comprehends .in its "range of adjustment one of the SQtSQOfi combination frequencies pro- "duced by the modulation of thereceived C lifrierwave's with the locally generated wave.the amplifier. "Afterfdetection'i d 0 f T o qu n y e y 'e D and audio frequency amplification in am-:

ble tuning condenser 62 is applied to the grid of modulatornM" together with ltheilocally generated wave supplied by way of. tap? 59 from; loscil'lator 0*. The combination .frequ'encies in the output of modulator 1M? are applied (either with or without further selectionfby means of jvairiable condenserf63, as

I desired) to th efinput circuit: of screen grid amplifier The amplified frequency corresponding to that for which variable con-7' denser 62is .set isselected'by variablecondenser 64L in the tuned plate circuit of the screen grid amplifier, and; iscapacitatively coupled, according to a well known circuit arrangement of screen grid amplifiers, with the inputjcircuit ofdetector D .j -The;audio 1.;If it is assumed or signaling] frequency components obtained by'demodulation in the detectorl) pass by 'wayivof audio frequency amplifier A to the loud speaker S.

cycles and that the local oscillator 'i'srsetto that the tuning range of frequencies for 'which variable condenser 61 is adapted extends from 550 to 1,500 kilo- ,iamg ss produce havinga frequency valuefof 100 kilocycle's, the'tuned-cir'c'uit controlled} by variable condenser 62 mjay have; a rangeof adjustmentiextending'from 450 kilocycles to trolled by variable condenser 64 (and also the tuning-circuit. controlled by variable condenser" 63, if" used) will be "adapted forf a ifrequ'en'eyfraiige of 550' to 71,500 -kilocycles corresponding to that-"of variable condenser coupled' a-nd coordii'iated; asindicated.

In the-circuit o'f-Fig; 8"the carrier waves" arereceived by theopen antenna65and ap W plied-to the} input circuit of modulator M 1,4:00 kilocycles; andthe-tuning circuit 'con- :7

through the mediuni of coupling transformer v 66." Modulator M is shown to beef the I modulating type employing grid condenser] 67 and grid leak path 68 in'its input circuit; Selection of the desired station ,jcarrier" wave is effected by tuningcondenser 69, and the selected wave together with the; locally generated wave from oscillator O intermodulate municated to the input circuit of amplifier A Further selection is eflected -by tuning Selected by variable condenserf70' "maybe' 'm grid type, and the modulation vfrequencies lowerfthan the corresponding received .;car=

and produce combination frequencies in the A modulator output circuit, these being comrier frequencies in, order-to take advantage of amore. favorable amplification factor in plifipr Ai the signal components of the.-

" It willlbe understood that, in accordance with usual practice, f the oscillator and radio 4- "V frequency stages of the rec'eivl'ng circuits that have beendescribedjare to be properly.

screenedrin' order to prevent undesirable coupling and feed backof energy. It will also be understood that proper and customary precautions are to be taken to ensure that the .modulating frequency vas supplied by the l q q l a o -i hall e a pure frequency, I ll l yfreefrom.harmonics.

- What is claimedis;

.1.'.The 1nethod-of. selective signal r'e'cep- 'tion, which, consists "in selecting one of a selected carrier wave with a locally, applied number of signal carrier waves' lying with- Wave of fixed frequency, lying outside saidrange and of'sucha frequency as to produce 7 w th said selected wave, side frequencies which are-readily, separable from'waves of 139 j "61, the tuning condensersloeingfmeclianically neighborhood of the frequencies of'said band and are non-coincident inyfrequency with each other or with side frequencies of opposite sign, and selecting and utilizing said side frequencies ofsaid one sign. I

.13. The method of selectively receiving car-rier waves, which consists 1n selecting 1ncoming carrierwaves, modulating said selected waves with asecond set of waves, selecting from the resulting products of modulation a third set of waves consisting-of side frequencies of only one sign, modulating said third set of waves with said second set of set of waves.

e 14; The methodof selectively receiving sig nal carrier waves of any'given frequencyi within a frequency band having a width at least as large as one of the frequencies there- 'in, which consists in selecting incoming signal carrier waves of desired frequency and largely excluding Waves of undesired frequency, limiting the frequency width of the band within which said selection can be made to a value which is not greater than twice the low frequency limit of said band, modulating said selected waves with another set of waves of a frequency not greater than said low frequency limit and not less than one-half the frequency width of said band, selecting side frequencies of only one of the two signs of side frequencies resulting from said modula tion, and utilizing said selected side frequen- 15. The method of high frequency amplification which consists in selectively receivinga wave, changing the frequency of said wave in one direction, preventing radiation of the resulting wave, changing the frequency of the resulting wave in the opposite direction, and increasing the voltage of the wave with each of said changes of frequency. I

16. The method of high frequency amplification, which consists in changing the frequency of a high frequency wave in one direction by a given amount, preventing radiation of the resulting wave, changing the frequency of the resulting wave by the same amount in the opposite direction, and in creasing the amplitude of thewave with each of said changes of frequency.

17. The method of carrier'wave amplification, which consists in changing the fre quency of the wave in one direction, preventing radiation of the resulting wave, changing the frequency of the resulting wave in the opposite direction, said frequency changes being by. inharmonic fractional amounts, and increasing the amplitude of I the wave with each of said changes of frequency. I I v V q 18. The method of selective carrier wave reception and amplification, which consists in changing thefrequency level of saidwave,

preventing radiation of the resulting wave,

selecting the wave at the changed level, re- 1 simultaneous adjustment of the different frequency levels of said wave in said stages.

20. The method of carrier wave ampllficatlon, which 'COIlSlStS m modulatlng' one or more carrier waves with a locally applied wave of fixed single frequency, modulating the side band or bands of one sign resulting from said modulation, with said locally applied wave, and utilizing in the resulting wave a side hand of opposite sign from that of said first-mentioned side band or hands.

21. The method of selective carrierwave reception and amplification, which consistsin c modulating the waves of a band'of carrier waves with a local wave of fixed frequency, selectingthe sidebands of frequencies of I only one sign resulting from said modulation,

restoring the frequency of said bands to the original carrier wave frequency values by modulating said selected side bands with said local "wave, and utilizingthe products'of I said second modulation. 7

22. The method of selective carrier wave reception and amplification, which consists in selectively receiving a carrier wave, modulating the same with a local wave of fixed 4 frequency to producea modulation product differing in frequency from the'frequency of the received carrier wave by an amount equal to the frequency of said local wave, re-' storing the frequency of said resultingwave r to the original frequency of the received carrier wave by modulating said modulation product with said local wav'e,and utilizing said second'modulation product.

23. In a carrier wave receivingv system,

means for'selectively receiving a range of carrier waves, a fixed frequency wave source,

a modulator for combining the received car rier waves and the fixed frequency wave to produce upper and lower amplifiedsets of signal bearing side bands, and means for suppressing one of said sets of side bands and for selectingand utilizing the other of said sets of side bands.

24. In a carrier wave receiving system, i.

waveslying within a certain frequency range,

a fixed frequency wave sourcefor generating a wave having a frequency lyingoutsidethe frequency range of the received carrier waves,

a modulator forcombining thereceived cars rier waves with said fixed frequency waveto produce a set ofupper and a set of lower side bands, and means for selecting and utilizing from one of said sets a combination frequency of any desired one of said carrier waves and for suppressing the corresponding combina-i' tion frequency in the other of said sets.

25. In a carrier wave receiving system,

-means for receiving carrier-waves within a certain range of frequencies, means for producinga localwave of fix'edfrequency lying" outside said range and of such a frequency 1 as to be capable of producing withsaidre ceived waves, side frequencies which are" readily separable from waves of said received frequency, a modulator, means for selectlng "one of said carrierwaves' and combining it 7 with'the fixed frequencyv wave in said modumodulator having an input I output circu1t,mea-ns for locallygeneratlnga wave of fixed frequency value, unicontrolled.

lator to produce a combination frequency, and

means for selecting and utilizing said combi nation frequency.

' 26. In a carrier wave variable tuning-devices coupledto said input circuit and said output circuit respectively and adapted'to maintain a fixed tuning dif ference between the 'sameequal to the frequency of said locally generated wave, means ,7 for receiving and applying "a signal carrier with "said locally generated wave togetherwave to the input circuit of said modulator'to amplify and change the frequency of said, carrier wave, and'means for utilizing the corrier jwave 1 derived receiving systemaa circuit and an responding changed frequency 1 signal car-f j 27.;In a carrierwave receiving "system, H I V 'V I 7 I meansforreceiving signal carrier waves, two

from the output circuit of said modulator'. j

modulators eachhavingan input circuit; and" an output circuit, means, fo'rflocally generatthe second'modulator, unitarily operated tum,

'inga waveof fixed frequency,rmeans for ap I, plying a signal carrier wave and said locally generated; wave .to 'thej input circuit of the "first'modulator, connections between the out-f "f" {putf'of thefirst modulator and' tlie input-of" ing devicesassociatedrespectively,withthe Y input ofthe first modulator; andthe COIlIlGC-Q tionsbetwe'en the output of the first modulator-andthe input of the second modulator,

said tuning devices being adapted to maintain I a fixed tuning difference between them equal; to the frequency 'of'said locallygenerated 35 wave, means, for modulating in the'se'cond i modulator al product of modulation of the, i first modulator with said locally generated wave, and means for utilizing the product of modulation of said second modulator.

'28., The method of selectively receiving carrler. Waves, WhlCh'COIlSlSlZS m selecting 11- coming carrier waves, modulating saidselectedwaves with a second set of waves, se-g lectingfrom the resulting products of, mod--r ulation a third set of wavesconsisting ofside frequencies offonly one sign,'modulating-said third set of wEWcS with said 'secondlset off-f I Q waves, selecting from the resulting products of modulation, ja fourth'set of waves consist ing of side frequencies of onlyone sign opposite to the-sign of said previously selected side frequencies, and utilizing said fourth set of waves. I v I so I EDWIN: swarm; 

